We propose in this research project to study patients with rheumatic diseases and experimental animals in which immune reactions to nuclear acidic protein antigens (NAPA), PM-1, RNP, Sm and MA, occur. The long-term objective of this study is to examine the immune reactivity to these antigens and its relationship to the rheumatic diseases: polymyositis-dermatomyositis, systemic lupus erythematosus, mixed connective tissue disease and other related rheumatic diseases. Specific objectives are: 1. Pursue Purification, Biochemical and Immunological Characterization and Inter-Relationships of PM-1, RNP, Sm and MA antigens. 2. Production of more Sensitive Immunological Assays, and of Immunological and Biochemical Probes. 3. Analyze the Expression and Localization of Nuclear Acidic Protein Antigens in Serum, Tissues and Cells. 4. Longitudinal Study and Selective In-Breeding of MRL Mouse Model. 5. Evaluation of T Suppressor (TS) and T Amplifier (TA) Function in Vivo in MRL Mice. 6. Evaluation of T and B Cell Function in Vitro in MRL Mice. 7. Induction of Tolerance in MRL Mice.